Chassis part consisting of fibre-reinforced plastics, equipped with an integrated sensor

ABSTRACT

The present invention pertains to a chassis part for connection and force transmission between a vehicle chassis of at least one wheel, consisting of fiber-reinforced plastics or plastic composite systems, preferably for a passenger car or utility vehicle.  
     The present invention is characterized in that at least one means for measuring forces acting on the chassis parts is integrated in the plastic portions of the chassis parts.

[0001] The present invention pertains to chassis parts for connectionand force transmission between a vehicle chassis and at least one wheel,consisting of fiber-reinforced plastics or plastic composite systems,preferably for a passenger car or utility vehicle.

[0002] Such chassis parts for connection and force transmission betweenthe vehicle chassis and the wheel, also called control arms, are known,in principle. Furthermore, it has been known, e.g., from DE 38 39 855 A1that lightweight components comprising a connection between structuralparts made of metal and plastic can be manufactured. It is problematicin such composite materials that the plastic portions, especiallyfiber-reinforced plastic components, may undergo brittle fracture underexcessively high loads. This means that such parts may abruptly losetheir strength and stability under an excessively high load. The use ofsuch composite materials in chassis control arms therefore represents acertain safety hazard, because, on the one hand, extremely high safetyrequirements are imposed here, but enormous forces may briefly act onthe chassis control arms because of unpredictable driving situations oraccident situations. However, such composite materials make possible anextremely low-weight and consequently energy-saving design, so that itis desirable for reasons of the efficient manufacture of vehicles to usesuch composite materials in chassis control arms as well.

[0003] The object of the present invention is therefore to design theabove-mentioned chassis parts such that a hazard-free and risk-free usein vehicles is possible.

[0004] This object is accomplished by the features of the independentpatent claims. Advantageous variants of the present invention are thesubject of subclaims.

[0005] The inventors have recognized that it is possible to recognizesymptoms of fatigue in time by the continuous monitoring of the forcesoccurring in these chassis parts and thus to guarantee sufficient safetyduring the use of composite materials for such chassis parts. Sinceplastics have a substantially greater elongation than metals at equalstrength, these materials are especially suitable for determining theload actually acting on them simply and accurately by means of wirestrain gauges or piezo elements. Since integration over time is alsopossible, it is also possible to detect symptoms of material fatiguethat are generated not only by peak loads but also by permanent loads.Moreover, it proved to be especially advantageous that not only areforce measurements possible as a result for monitoring the service lifeof these chassis parts, but the measured force values can also beutilized in electronic control devices, preferably for stabilizing thedriving or position of vehicles.

[0006] Corresponding to the idea of the present invention, the inventorsconsequently propose to improve chassis parts for connection and forcetransmission between a vehicle chassis and at least one wheel,consisting of fiber-reinforced plastics or plastic composite systems,preferably for a passenger car or a utility vehicle, in such a way thatat least one means for measuring forces acting on the chassis parts isintegrated in the plastic portions of the chassis parts.

[0007] Chassis parts are basically lever constructions, which are alsosubject to higher loads and especially accelerations than the rest ofthe vehicle in a jerky and shock-like manner, especially if they areso-called control arms. These accelerations occurring can be measuredwith an acceleration sensor. If we now assume that certain accelerationsover a defined period of time describe a path traveled, abuse of thecontrol arm, e.g., high-speed travel over a curb, can be inferred. Eventhough this is not a direct force measurement, it is neverthelesssufficient for identifying states of abuse.

[0008] As was mentioned above, wire strain gauges or piezo elements, bymeans of which the forces occurring and acting on the chassis parts canbe determined in an electronic manner, may be mentioned here especiallyadvantageously.

[0009] In a special design of the chassis parts according to the presentinvention, the means for measuring the acting forces are arranged suchthat they can record forces along at least two and preferably threeindependent axes. As a result, it is possible to define the actingforces either in one plane or even in space.

[0010] Another manner of measuring the load acting on a force connectionstrut may be to embed a fiber-optic light guide in a plastic, in whichcase the transmission changes in individual modes as soon as the plasticis bent under load. Thus, the bending stress in the control arm can beinferred from the measurement of frequency band shifts, e.g., theextinction of individual modes.

[0011] Corresponding to the basic idea of the present invention, theinventors also propose a vehicle with the above-mentioned chassis parts,wherein at least one means for measuring the acting forces is coupledwith an electronic control device for stabilizing the travel and/or theposition of the vehicle, especially by acting on driving or brakingelements. Such control devices may be, e.g., the prior-art ESP(Electronic Stability Program) or even a simple headlight levelingcontrol of the vehicle headlights.

[0012] Furthermore, a vehicle according to the present invention mayalso be designed such that at least one means for measuring the actingforces is coupled with an electronic documentation device for themeasured forces. This electronic documentation device, which comprises,e.g., a simple electronic memory, in which the measured values arestored electronically, now also makes it possible to recognize loadsthat occur later. Another possibility is to also carry out an evaluationof the measured values, e.g., with respect to the maxima read out, or amore complex calculation of an integrated load and consequently of thelife expectancy still present, in the electronic documentation device.This may possibly also be performed combined with a temperature sensor,because there likewise are dependences between the strength of theparticular chassis part and the current body temperature of the chassispart, which should be taken into account especially in case of the useof plastics. The load-bearing capacity of plastics has a substantiallystronger temperature dependence than metals.

[0013] It is especially advantageous in the sense of the idea of thepresent invention if the electronic documentation device is integratedin the electronic control device for stabilizing the driving and/or theposition of the vehicle. This leads to the possibility of having tocalculate the currently occurring forces only once and to use them atthe same time for the life expectancy, on the one hand, and forstabilizing the driving and/or the position of the vehicle, on the otherhand.

[0014] Since information is obtained on the durability of the chassispart based on the knowledge of the loads on the corresponding chassispart, it may, furthermore, be advantageous to provide means for warningwhen preset maximum loads are exceeded and/or a maximum service life hasbeen reached. The measured data are consequently used for twoapplications at the same time. This results in a synergistic effect dueto the elimination of the need for additional sensors for controllingthe overload on the control arm or for the determination of the chassisparameters for an electronic drive or position stabilization.

[0015] In a continuation of this idea of the present invention, theinventors propose, furthermore, that the documentation device also havemeans for locking the vehicle when the above-mentioned preset maximumloads or the maximum service life of an essential chassis part areexceeded.

[0016] Due to the outfit of chassis parts according to the presentinvention, it is now also possible to manufacture control arms that arerelevant for safety from fiber-reinforced plastics and to use themwithout safety hazards. If the control arms are manufactured accordingto an injection molding process or an RTM-like process (RTM=ResinTransfer Molding), the integration of prefabricated sensors as insertscan be accomplished very easily. Control arms from other materials ormaterial composite systems, which have a high local elongation due totheir design, are suitable as well. Sensors can be integrated in thiscase in the control arm in a simple manner in appropriate areas, e.g.,where high local loads occur. The sensors may assume two functions,namely, they may be used, on the one hand, for the continuousmeasurement of the forces and consequently for providing data for anelectronic chassis control, and, on the other hand, for monitoring toshow whether overloads that could damage the control arm itself occur.

[0017] The information that makes possible the diagnosis of the state ofthe chassis is thus made available by the process described. Inparticular, such a diagnosis may be meaningful after accidents, inwhich, e.g., no visible damage can be recognized on chassis parts, butit may be assumed based on the forces measured that structural damagemust have occurred inside such parts.

1. Chassis part for connection and force transmission between a vehiclechassis and at least one wheel of a motor vehicle, consisting offiber-reinforced plastics or plastic composite systems, characterized inthat at least one means for measuring forces acting on the chassis partis integrated in the plastic portion of the chassis part.
 2. Chassispart in accordance with claim 1 above, characterized in that at leastone means for measuring the acting forces is a wire strain gauge, apiezo element, an acceleration sensor or a fiber-optic light guideembedded in the plastic of the chassis part.
 3. Chassis part inaccordance with one of the above claims, characterized in that the meansfor measuring the acting forces are arranged such that they can recordforces along at least two and preferably three independent axes. 4.Vehicle with a chassis part having the features in accordance with oneof the above claims, characterized in that at least one means formeasuring the acting forces is coupled with an electronic control devicefor stabilizing the driving and/or the position of the vehicle,especially by action on driving or braking elements (e.g., ESP). 5.Vehicle in accordance with the preamble of claim 4 above or inaccordance with claim 4 above, characterized in that at least one meansfor measuring the acting forces is coupled with an electronicdocumentation device for the measured forces.
 6. Vehicle in accordancewith claim 5 above, characterized in that the electronic documentationdevice is integrated within the electronic control device forstabilizing the driving and/or the position of the vehicle.
 7. Vehiclein accordance with one of the claims 5 or 6 above, characterized in thatthe documentation device has means for warning when preset maximum loadsand/or the service life are exceeded.
 8. Vehicle in accordance with oneof the claims 5 through 7 above, characterized in that the documentationdevice has means for locking the vehicle when preset maximum loads areexceeded.
 9. Use of means integrated in chassis parts made of plastic orcomposite materials for measuring forces acting on the chassis parts,preferably in accordance with one of the claims 1 through 3 above, forchecking the service life of these chassis parts and for collectingmeasured values for electronic control devices, especially for theheadlight leveling control and/or for the stabilization of the drivingand the position of a vehicle.